In a cordless power tool, it has been demanded that a battery functioning as a power supply should be increased in capacity and be reduced in weight; and, to meet this demand, recently, there has been expected and gradually employed a lithium battery which is high in power density.
In the lithium battery, when it is overcharged or over-discharged, there is a fear that the lithium battery can be deteriorated or can ignite. In view of this, there is provided a protection IC for monitoring the overcharging and over-discharging of the respective cells included in the battery pack. Specifically, when the battery voltage of each battery cell is equal to or higher than a first given voltage value or equal to or lower than a second given voltage value, the protection IC outputs a detect signal and, based on the detect signal, a charging and discharging path is cut off to thereby secure a safety measure for the battery, that is, the overcharging or over-discharging of the battery can be prevented (see JP-A-6-141479).